In electrophotography, an electric latent image is formed on an image carrier, the latent image is then developed with a toner, the toner image is transferred onto a transfer material such as paper, and the transferred image is fixed by means of heating, pressing, and the like. The toner used can be not only the conventional monochromatic black toner. Thus, in order to form a full-color image, toners of a plurality of colors are used to form an image.
A toner can be in the form of a two-component developing agent in which the toner is used in a mixture with carrier particles, or in the form of a single-component developing agent using a magnetic toner or a nonmagnetic toner. The toners are usually manufactured by a kneading and grinding method. With the kneading and grinding method, a binder resin, a pigment, a parting agent such as wax, and a charge controlling agent are melt kneaded, cooled, finely ground, and classified to produce the desired toner particles. The toner can be obtained by adding inorganic and/or organic microparticles, according to the object, to the surface of toner particles manufactured by the kneading and grinding method.
In the case of toner particles manufactured by the kneading and grinding method, the shape is difficult to control intentionally. In particular, in the case a material with a high grinding ability is used, fine pulverization easily proceeds and in a two-component developing agent, the finely pulverized toner fixedly adheres to the carrier surface, whereby the charge deterioration of the developing agent is accelerated, whereas in the case of a single-component developing agent, the finely pulverized toner is scattered or developing ability thereof degrades according to changes in the toner shape and the image quality is deteriorated. Further, if grinding occurs at the interface of binder resin and wax, the wax separates from the toner and easily contaminates the developing roller, image support, and carrier, and the reliability of the developing agent decreases.
With the foregoing in view, an emulsion polymerization and agglomeration method was recently suggested in JP-A-63-282752 or JP-A-6-250439 as a method for manufacturing a toner in which the shape and surface composition of toner particles are intentionally controlled.
With the emulsion polymerization and agglomeration method, a resin dispersion is produced by emulsion polymerization, a colorant dispersion is also produced in which a colorant is dispersed in a solvent, the two dispersions are mixed to form agglomerated particles equal in diameter to toner particles, and then toner particles are obtained by heating-induced fusion. With the emulsion polymerization and agglomeration method, the toner shape can be freely controlled from indeterminate to spherical by selecting the heating temperature conditions.
With the emulsion polymerization and agglomeration method, the dispersion comprising at least the resin microparticles and the colorant dispersion can be obtained by agglomeration and fusion under the predetermined conditions. However, the types of resins that can be synthesized in the emulsion polymerization and agglomeration method are limited, and although this method can be advantageously used for the manufacture of styrene-acryl copolymers, it cannot be applied to polyester resins that are known to have good fixing ability.
By contrast, a phase inversion emulsification method in which a pigment dispersion, etc., is added to a solution using an organic solvent and then water is added is known as a method for manufacturing a toner using a polyester resin, but with this method, the organic solvent has to be removed and recovered. A method for manufacturing microparticles by mechanical stirring in an aqueous medium, without using an organic solvent, is suggested in JP-A-9-311502, but with this method a resin in a molten state has to be supplied to a stirring apparatus and is difficult to handle. Furthermore, the level of freedom with respect to shape control is low and the toner shape cannot be freely controlled from indeterminate to spherical.